CN115497516A - Holographic storage light path system and light beam calibration method thereof - Google Patents

Holographic storage light path system and light beam calibration method thereof Download PDF

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Publication number
CN115497516A
CN115497516A CN202110673706.4A CN202110673706A CN115497516A CN 115497516 A CN115497516 A CN 115497516A CN 202110673706 A CN202110673706 A CN 202110673706A CN 115497516 A CN115497516 A CN 115497516A
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China
Prior art keywords
light
signal
servo
calibration
storage medium
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CN202110673706.4A
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Chinese (zh)
Inventor
胡德骄
刘义诚
田军
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Guangdong Amethyst Information Storage Technology Co ltd
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Guangdong Amethyst Information Storage Technology Co ltd
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Priority to CN202110673706.4A priority Critical patent/CN115497516A/en
Priority to KR1020220073794A priority patent/KR20220168996A/en
Priority to US17/843,795 priority patent/US20220404766A1/en
Priority to EP22179579.2A priority patent/EP4116971A3/en
Priority to JP2022097884A priority patent/JP2023001090A/en
Publication of CN115497516A publication Critical patent/CN115497516A/en
Withdrawn legal-status Critical Current

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    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/0005—Adaptation of holography to specific applications
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0402—Recording geometries or arrangements
    • G—PHYSICS
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    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0486—Improving or monitoring the quality of the record, e.g. by compensating distortions, aberrations
    • G—PHYSICS
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    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2202—Reconstruction geometries or arrangements
    • G03H1/2205—Reconstruction geometries or arrangements using downstream optical component
    • G—PHYSICS
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    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2249—Holobject properties
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    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
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    • G11B7/007—Arrangement of the information on the record carrier, e.g. form of tracks, actual track shape, e.g. wobbled, or cross-section, e.g. v-shaped; Sequential information structures, e.g. sectoring or header formats within a track
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    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
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    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
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    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0938—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following servo format, e.g. guide tracks, pilot signals
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    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
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    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1378—Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/2403—Layers; Shape, structure or physical properties thereof
    • G11B7/24047—Substrates
    • G11B7/2405—Substrates being also used as track layers of pre-formatted layers
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/16—Processes or apparatus for producing holograms using Fourier transform
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0402—Recording geometries or arrangements
    • G03H2001/0434—In situ recording when the hologram is recorded within the device used for reconstruction
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0443—Digital holography, i.e. recording holograms with digital recording means
    • G03H2001/045—Fourier or lensless Fourier arrangement
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2202—Reconstruction geometries or arrangements
    • G03H2001/2244—Means for detecting or recording the holobject
    • G03H2001/2247—Means for detecting or recording the holobject for testing the hologram or holobject
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2222/00—Light sources or light beam properties
    • G03H2222/40—Particular irradiation beam not otherwise provided for
    • G03H2222/42—Reference beam at recording stage
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2222/00—Light sources or light beam properties
    • G03H2222/40—Particular irradiation beam not otherwise provided for
    • G03H2222/43—Object beam at recording stage
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2222/00—Light sources or light beam properties
    • G03H2222/40—Particular irradiation beam not otherwise provided for
    • G03H2222/45—Interference beam at recording stage, i.e. following combination of object and reference beams
    • G—PHYSICS
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    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2223/00—Optical components
    • G03H2223/20—Birefringent optical element, e.g. wave plate
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2225/00—Active addressable light modulator
    • G03H2225/52—Reflective modulator
    • G—PHYSICS
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    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2250/00—Laminate comprising a hologram layer
    • G—PHYSICS
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    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2270/00—Substrate bearing the hologram
    • G03H2270/20—Shape
    • G03H2270/22—Disc shaped
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    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B2007/240025—Record carriers characterised by shape, structure or physical properties, or by the selection of the material for storing optical interference patterns, e.g. holograms

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Optical Head (AREA)
  • Holo Graphy (AREA)

Abstract

The invention provides a holographic storage optical path system and a beam calibration method thereof. The recording unit comprises a movable Fourier lens, and the positions and the irradiation angles of the signal light spot and the reference light spot are adjusted by moving the Fourier lens. The servo unit includes a collimating lens for adjusting horizontal and vertical positions of the servo light spot to locate the servo light spot at an optimal relative position to the signal light and the reference light. The method for beam alignment comprises the following steps: (1) Before recording the data hologram, recording a calibration hologram at a calibration hologram bit mark on a track of a storage medium; (2) Before the data hologram is reproduced, the calibration hologram is used, the signal-to-noise ratio of the hologram reproduction is optimized by adjusting the calibration lens and the second Fourier lens, and then the data hologram is reproduced.

Description

Holographic storage light path system and light beam calibration method thereof
Technical Field
The invention relates to the technical field of optical storage, in particular to a holographic storage light path system and a light beam calibration method thereof.
Background
Holographic optical storage uses interference of optical waves to record data page information in a form of hologram in a photosensitive medium, and compared with the conventional optical storage technology, the holographic optical storage has the advantages of large storage capacity, high data transmission rate, short addressing time and the like. In the holographic optical storage technology, a laser beam is divided into two beams, namely reference light and signal light, wherein the signal light carries data page information after being transmitted or reflected by a spatial light modulator, and the signal light and the reference light are interfered in a photosensitive material layer of a storage medium and exposed to form a hologram, so that information is recorded.
The holographic storage medium is internally provided with an address layer, and annular or spiral grooves or ridge-shaped light paths are distributed on the address layer; the annular groove or the convex ridge is detected by the servo light sensing system to realize accurate positioning, so that quick and convenient data access and storage are realized. The introduction of the servo light path into the holographic optical storage light path system can effectively improve the storage and retrieval efficiency of data.
When reading the hologram, it is necessary to irradiate the same reference light as that used in recording to reproduce the hologram stored in the hologram material; if the storage medium is deformed, the irradiation position and angle of the reproduced reference light are adjusted to enable the wave vector to meet the Bragg matching condition of the hologram, so that the signal light is effectively reproduced. In addition, in order to ensure that the data can be completely read when the holographic optical disk recorded with data is read on the same holographic optical drive or other holographic optical drives, the servo beam and the reference beam must be calibrated. Therefore, it is necessary to establish an effective calibration system for calibrating the servo beam and the reference beam so that the optical head can read the data in the hologram completely during high speed movement.
In the holographic optical storage systems designed by other companies, no matter off-axis or on-axis holographic technology is used, a servo light path system of the holographic optical storage system has no calibration mechanism, so that the difficulty of completely reading data is high, and the compatibility of different devices is poor.
Disclosure of Invention
The present invention is directed to overcoming at least one of the above-mentioned disadvantages of the prior art, and to provide a holographic storage optical path system and a beam calibration method thereof.
In one aspect, the present invention provides a holographic storage optical path system including a storage medium, a recording unit, an imaging unit, and a servo unit.
The storage medium comprises an address layer and a recording layer, wherein the address layer consists of a plurality of light paths, and a plurality of data holographic bit marks and calibration holographic bit marks are arranged on the light paths; a hologram for positioning the recorded data and a calibration hologram for calibrating the optical path, respectively.
The data holographic bit marks and the calibration holographic bit marks are located in different regions of the track, respectively.
The recording unit is used for generating signal light and reference light, respectively irradiating the signal light and the reference light to a storage medium at a certain angle, and generating a hologram in a recording layer of the storage medium through interference exposure; the recording unit comprises a signal light path, a reference light path and a relay lens group for adjusting the signal light and the reference light beams; the relay lens group includes a fixed first Fourier lens and a movable second Fourier lens, and the irradiation positions and angles of the signal light and the reference light are adjusted by moving the second Fourier lens.
The imaging unit is used for converting the reproduced light diffracted by the reference light into a data page image and collecting the data page image; comprising a fourth fourier lens for imaging and an image sensor for collecting the data page image, i.e. the hologram reconstruction image, and analyzing the diffraction efficiency and the signal-to-noise ratio.
The servo unit is used for ensuring that the distance between the optical head and the storage medium is constant and ensuring that the signal light and the reference light move along the track in the moving process of the optical head relative to the storage medium, and can also accurately position the recording or reproducing position and comprises a servo laser, a beam splitting module, a calibration lens and a signal detection module. The servo laser is used for generating servo light; the beam splitting module is used for transmitting the servo light beam incident to the storage medium from the laser and reflecting the servo light beam returned by the storage medium to the signal detection module; the calibration lens is used for adjusting the horizontal and vertical positions of the servo light spots; the signal detection module is used for detecting the servo light returned by the storage medium and analyzing the servo light to obtain a servo signal.
The position of a servo light spot is calibrated by moving the calibration lens, and the irradiation positions and angles of the reference light and the signal light are adjusted by moving the second Fourier lens. During recording, the collimating lens and the second Fourier lens are moved to initial positions, the servo light is converged on the address layer, and interference areas of the reference light and the signal light effectively cover the storage medium. In the reading process, the second Fourier lens is moved, the irradiation position and the irradiation angle of the reference light are adjusted, the diffraction efficiency and the signal-to-noise ratio of the hologram reach the maximum value, and the servo light spot is calibrated through the calibration lens and is positioned on the holographic position mark. Thus, when the servo light spot is located on the holographic bit mark, the reproduced reference light can always reproduce the recorded data page information with the best signal-to-noise ratio.
In order to effectively utilize laser emitted by the servo laser to generate a servo signal, a beam splitting module is used in a servo light path to regulate and control the polarization state and the traveling path of servo light. Preferably, the beam splitting module includes a first half wave plate, a first polarization beam splitter and a 1/4 λ plate, the first half wave plate adjusts the servo light emitted by the servo laser to be p-polarized servo light, the p-polarized servo light can completely transmit through the first polarization beam splitter, the 1/4 λ plate adjusts the p-polarized servo light transmitted from the first polarization beam splitter to be circularly polarized servo light, and adjusts the circularly polarized servo light reflected back from the storage medium to be s-polarized servo light, the s-polarized servo light can be completely reflected by the first polarization beam splitter to the signal detection module, and detection and analysis are performed, and the signal detection module is preferably a photodetector.
The recording unit comprises a light source module, a signal loading module and an optical head module. The light source module outputs signal light and reference light. And the signal loading module is used for loading the information in the spatial light modulator into the signal light. The optical head module is used for enabling the signal light, the reference light and the servo light to be incident to the storage medium at a certain angle, and the signal light and the reference light are subjected to interference exposure on the storage medium to generate a hologram.
The optical head module comprises a dichroic mirror which reflects the servo light and transmits the read-write light, so that the servo light and the read-write light are combined.
The light source module comprises a light path; the signal loading module comprises one path of light path or two paths of light paths; the optical head module comprises one optical path or two optical paths.
When the signal loading module comprises a light path, the light path of the signal light and the light path of the reference light are overlapped on the light path, the relay lens group is shared, and the irradiation positions and angles of the signal light and the reference light can be adjusted simultaneously by moving the second Fourier lens. When the signal loading module comprises two paths of light paths, the signal light path and the reference light path respectively comprise independent relay lens groups, and the second Fourier lens for moving the signal light path can independently adjust the irradiation position and the angle of the signal light; the second Fourier lens moving the optical path of the reference light can independently adjust the irradiation position and the angle of the reference light.
When the optical head module comprises a light path, the signal light path, the reference light path and the servo light path share one objective lens, and irradiate the storage medium in a direction vertical to the surface of the storage medium. When the optical head module includes a first optical path and a second optical path, the first optical path partially overlaps with the servo optical path. The first optical path is the reference light path when passing through the reference light, i.e. the reference light path partially overlaps the servo light path. At this time, the reference light and the servo light share one objective lens, through which the storage medium is irradiated in a direction perpendicular to the surface of the storage medium. According to another preferred embodiment, the first optical path passes through the signal light, and in this case, the first optical path is a signal light optical path, that is, the signal light optical path partially overlaps with the servo light optical path. At this time, the signal light and the servo light share one objective lens, and are incident on the storage medium through the objective lens in a direction perpendicular to the surface of the storage medium, respectively.
The invention also provides a light beam calibration method, which is used for recording the calibration hologram at the calibration holographic bit mark on the track of the storage medium before recording the data hologram. Before the data hologram is reproduced, the calibration hologram is used, a servo light spot is ensured to be positioned at a calibration holographic bit mark by adjusting a calibration lens and a second Fourier lens in a holographic storage optical path system, the irradiation position and the angle of a reference beam are changed to ensure that the reproduction signal-to-noise ratio of the hologram is optimal, and then the data hologram is reproduced.
The invention detects the diffraction efficiency and the signal-to-noise ratio of the hologram through the image sensor, and when the diffraction efficiency and the signal-to-noise ratio of the hologram reach the maximum value, the reference beam is considered to be adjusted to be the best.
The method for inscribing the calibration hologram and the data hologram specifically comprises the following steps:
s11, moving the calibration lens and the second Fourier lens to an initial position, so that a hologram generated by interference exposure of reference light and signal light is effectively positioned on a recording layer of a storage medium under the condition that a servo light spot is focused on an address layer;
s12, fixing a calibration lens and a second Fourier lens, moving a storage medium to enable a servo light spot to be located at a calibration holographic bit mark, and recording a calibration hologram at the calibration holographic bit mark;
s13, moving the storage medium to enable the servo light spot to be located at the other calibration holographic bit mark, and recording the next calibration hologram at the calibration holographic bit mark;
s14, repeating the step S13 for a plurality of times to ensure that a plurality of calibration holograms are successfully recorded;
s15, moving the storage medium to enable the servo light spot to be located at the data holographic bit mark, and recording a data hologram at the data holographic bit mark;
s16, moving the storage medium to enable the servo light spot to be located at the other data holographic bit mark, and recording the next data hologram at the data holographic bit mark;
s17, repeating the step S16, and recording the whole disc of data hologram;
in step S11, the method for determining the initial positions of the calibration lens 50 and the second fourier lens 202 is as follows: the optical path simulation design ensures that the servo light spot is on the plane of the track of the storage medium 6 (i.e. the address layer), and the interference area of the reference light and the signal light can effectively cover the storage medium 6, and the positions of the collimating lens 50 and the second fourier lens 202 at this time are the initial positions.
Before the data hologram is reproduced, the method for reading the position and the reference beam by moving the storage medium, the calibration lens and the second fourier lens and the method for reading the data hologram specifically include:
s21, moving a storage medium, moving the optical head to the position near the calibration holographic bit mark, and fixing the position of the calibration lens;
s22, adjusting the reference light wavelength and finely adjusting the positions of the second Fourier lens and the storage medium, and fixing the position of the second Fourier lens and the reference light wavelength when the diffraction efficiency and the signal-to-noise ratio of the calibration hologram at the calibration holographic bit mark are optimal;
s23, moving the position of the calibration lens to enable the servo light spot to be located at the position of the calibration holographic bit mark and fixing the position of the calibration lens;
s24, moving the storage medium to enable the servo light spot to be located at the next calibration holographic bit mark, and reproducing a calibration hologram at the calibration holographic bit mark;
s25, repeating the step S24 for a plurality of times to ensure that the reproduced signal-to-noise ratio of the plurality of calibration holograms meets the highest signal-to-noise ratio requirement after the second Fourier lens and the calibration lens are fixed;
s26, moving the storage medium, enabling the servo light spot to be located at the data holographic bit mark, and reproducing a data hologram at the data holographic bit mark;
and S27, repeating the step S26 to reproduce the whole disc of data hologram.
When the servo light spot is positioned in the middle of the calibration holographic bit mark or the data holographic bit mark, the track locking error signal and the tangential push-pull signal are both positioned at a zero value between a positive maximum value and a negative maximum value.
The track locking error signal is used for detecting the condition that the servo light spot deviates from the track, and when the servo light spot is positioned on the central line of the track, the track locking error signal is 0; when the servo light spot gradually deviates from the light track, the track locking error signal gradually tends to a maximum value or a minimum value; when the servo spot is completely off track, the tracking error signal becomes 0.
The tangential push-pull signal is used for detecting a holographic bit mark of a track, the holographic bit mark can be a notch, and when a servo light spot is positioned in the middle of the notch, the tangential push-pull signal is 0; when the servo light spot gradually deviates from the notch, the tangential push-pull signal gradually tends to a maximum value or a minimum value; when the servo light spot is completely out of the notch, the tangential push-pull signal becomes 0.
Compared with the prior art, the invention has the beneficial effects that:
the holographic storage optical path system is provided with a servo unit, addresses on a storage medium are addressed and positioned through the servo unit, and a hologram is stored in a designated position of the storage medium. In the reading process, the irradiation position and angle of the reference light can be adjusted by moving the second Fourier lens, and the diffraction efficiency and the signal-to-noise ratio of the hologram reach the maximum value by combining the wavelength and the movement of the storage medium. After the diffraction efficiency and the signal-to-noise ratio are optimized to the maximum values, the horizontal position and the vertical position of a servo light spot are adjusted through a calibration lens in a servo unit, so that the holographic bit mark can be locked by the servo light again, and the data page information can be completely reproduced by the reference light on the whole storage medium when the servo optical disk is positioned on the holographic bit mark. By the calibration method, even if the medium shrinks and expands, the data in the medium can be accurately read; meanwhile, the compatibility of reading the data stored in the hologram among different devices is enhanced.
Drawings
Fig. 1 is a holographic storage optical path system according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of convergence of a servo light spot and a reference light spot.
Fig. 3 is a holographic storage optical path system according to another embodiment of the present invention.
Fig. 4 is a schematic diagram of convergence of the servo light spot and the signal light spot.
Fig. 5 is a holographic storage optical path system according to another embodiment of the present invention.
FIG. 6 shows a holographic storage optical path system according to another embodiment of the present invention
Fig. 7 is a schematic diagram of a storage medium structure.
FIG. 8 is a block diagram of a positioning calibration process during data hologram recording.
FIG. 9 is a block diagram of a positioning calibration process for reading a data hologram.
Fig. 10 is a diagram showing the variation of the track-lock signal and the tangential push-pull signal with the position of the servo light spot.
Detailed Description
The drawings are only for purposes of illustration and are not to be construed as limiting the invention. For a better understanding of the following embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
Fig. 1 shows a holographic storage optical path system. The holographic-memory optical path system in the present embodiment includes a storage medium 6, a recording unit, an imaging unit 5, and a servo unit 3.
The recording unit is used for generating signal light 62 and reference light 61, and respectively making them incident into the storage medium 6 at a certain angle, and making interference exposure on the recording layer 120 of the storage medium 6 to produce hologram. The recording unit includes a signal light path, a reference light path, and a relay lens group. The relay lens group includes a fixed first fourier lens 201 and a movable second fourier lens 202, and the irradiation positions and angles of the signal light and the reference light are adjusted by moving the second fourier lens 202.
The imaging unit 5 comprises a camera 130, and the camera 130 is configured to capture the reproduced data page and monitor the diffraction efficiency and the signal-to-noise ratio of the reproduced data page, and if the diffraction efficiency and the signal-to-noise ratio are low, adjust the positions of the second fourier lens 202 and the storage medium 6 until the maximum value is reached. In order to convert the frequency domain light field of the data page reproduced by the reference light into spatial domain light field imaging, a fourth fourier lens 103 is arranged in front of the camera 130 to perform inverse fourier transformation on the frequency domain light field and project the spatial domain image onto the image sensor target surface of the camera.
The servo unit 3 comprises a servo laser 10, a beam splitting module, a movable collimating lens 50 and a signal detection module 40. The servo laser 10 is used for generating servo light 70; the beam splitting module is used for transmitting the servo light 70 incident to the storage medium 6 from the laser and reflecting the servo light 70 returned by the storage medium to the signal detection module 40; the collimating lens 50 is used for adjusting the horizontal and vertical positions of the servo light spot; the signal detection module 40 is used for detecting the servo light returned by the storage medium 6 and analyzing the servo light to obtain a servo signal.
As shown in fig. 2 or 4, the servo light spot is located on the address layer, i.e., the inner surface of the substrate 112, by moving the collimating lens 50 in the present embodiment. In the recording process, the second fourier lens 202 and the storage medium 6 are moved to the initial position, so that the interference area of the reference light 61 and the signal light 62 is ensured to effectively cover the storage medium; during reading, the second fourier lens 202 and the storage medium 6 are moved, the irradiation position and angle of the reference light 61 are adjusted, the diffraction efficiency and the signal-to-noise ratio of the hologram reach maximum values, and the servo light spot is collimated by the collimating lens 50 to be located on the holographic bit mark. Thus, when the servo light spot is located on the holographic bit mark, the reproduced reference light can always reproduce the recorded data page information with the best signal-to-noise ratio.
In this embodiment, the beam splitting module of the servo unit 3 specifically further includes a first half-wave plate 164, a first polarization beam splitter 173, and a 1/4 λ plate 21, where the first half-wave plate 164 adjusts the servo light 70 emitted by the servo laser 10 into p-polarized servo light 70, and the p-polarized servo light 70 can completely transmit through the first polarization beam splitter 173. The 1/4 λ plate 21 adjusts the p-polarized servo light transmitted from the first polarization beam splitter into the circularly polarized servo light 70, and adjusts the circularly polarized servo light reflected back from the storage medium into the s-polarized servo light 70, and the s-polarized servo light 70 can be completely reflected by the first polarization beam splitter 173 to the photodetector 40 and be detected and analyzed.
The recording unit according to the present embodiment includes a light source module 1, a signal loading module 2, and an optical head module 4.
The light source module 1 is configured to output signal light 62 and reference light 61. The signal loading module 2 is configured to load the data information in the spatial light modulator 190 into the signal light 62. The optical head module 4 is configured to inject the signal light 62, the reference light 61, and the servo light 70 into the storage medium 6 at a certain angle, and the signal light and the reference light are subjected to interference exposure on the storage medium 6 to generate a hologram.
Preferably, the signal loading module 2 includes a light path, the signal light path 62 and the reference light path 61 share a relay lens group, and the second fourier lens is moved to adjust the irradiation position and angle of the signal light and the reference light simultaneously.
In this embodiment, the optical head module 4 includes two optical paths, and the third polarization beam splitter 172 transmits the reference light 61 in the p-polarization direction to the first optical path and reflects the signal light in the s-polarization direction to the second optical path. The p-polarized reference light becomes s-polarized reference light after passing through the second half-wave plate 163. The first optical path includes a dichroic mirror 80 that reflects the servo light 70 and transmits the reference light 61, thereby combining the servo light and the reference light. In the first optical path, the reference light and the servo light share an objective lens 101, through which the storage medium is perpendicularly irradiated. In the second optical path, the signal light in the s-polarization direction is converted into a frequency domain by the third fourier lens 102, and enters the storage medium 6 at a certain included angle with the surface of the storage medium.
The signal light and the reference light having the same s-polarization direction incident on the storage medium 6 are subjected to interference exposure at a recording position where the servo unit 3 is positioned in the recording layer 120 of the storage medium 6 to form a hologram, thereby completing recording of information.
During reproduction, the spatial light modulator 190 has no input signal, only the reference light irradiates on the hologram of the recorded information in the storage medium 6, the obtained diffracted light continuously propagates along the propagation direction of the original signal light after passing through the storage medium, and the reproduced data information is collected through the imaging unit 5.
Fig. 3 provides another embodiment, in which the signal loading module 2 includes a light path, the signal light path 62 and the reference light path 61 share a relay lens group, and the second fourier lens is moved to adjust the irradiation positions and angles of the signal light and the reference light simultaneously.
The optical head module 4 includes two optical paths, and when the third half-wave plate 162 is removed, the third polarization beam splitter 172 transmits the signal light in the p-polarization direction to the first optical path, and reflects the reference light in the s-polarization direction to the second optical path. The first optical path includes a dichroic mirror 80 that reflects the servo light 70 and transmits the signal light 62, thereby combining the servo light and the signal light. In the first optical path, the signal light is converted into s-polarization after passing through the second half-wave plate 163; the signal light and the servo light vertically enter the surface of the storage medium through the same third Fourier lens 102. In the second optical path, the reference light in the s-polarization direction is converged by the first objective lens 101 into a reference light spot, and the reference light spot and the horizontal plane of the storage medium form a certain included angle and is incident to the storage medium 6.
The signal light spot and the reference light spot having the same s-polarization direction incident to the storage medium 6 are subjected to interference exposure at recording positions where the servo units are located in the recording layer 120 of the storage medium to form holograms, thereby completing recording of information.
During reproduction, the spatial light modulator 190 has no input signal, only the reference light irradiates on the hologram recording information in the storage medium, the obtained diffracted light continuously propagates along the propagation direction of the original signal light after passing through the storage medium, and the reproduced data information is collected through the imaging unit 5.
The servo unit and the imaging unit in this embodiment are the same as the servo optical path and the imaging unit in the embodiment described in fig. 1, and will not be described here.
Fig. 5 provides another embodiment, in which the light source module 1 includes a light path, and the signal light path and the reference light path are overlapped. The signal loading module 2 includes two optical paths, the signal light optical path 62 and the reference light optical path 61 have independent relay lens groups respectively, and the irradiation positions and angles of the signal light 62 and the reference light 61 can be adjusted by moving the second fourier lens 202 and the second fourier lens 204 respectively.
The optical head module 4 includes two optical paths, and the first optical path includes a dichroic mirror 80, which reflects the servo light 70 and transmits the reference light 61, thereby combining the servo light and the reference light. In the first optical path, the reference light path and the servo light path share an objective lens 101, through which the storage medium is irradiated in a direction perpendicular to the surface of the storage medium. In the second optical path, the signal light is converged into a signal light spot by the third fourier lens 102, and the signal light spot and the horizontal plane of the storage medium form a certain included angle and is incident to the storage medium 6.
The signal light spot and the reference light spot having the same p-polarization direction incident on the storage medium 6 are subjected to interference exposure at recording positions where the servo units are located in the recording layer 120 of the storage medium to form holograms, thereby completing recording of information.
During reproduction, the spatial light modulator 190 has no input signal, only the reference light irradiates on the hologram recorded in the storage medium, the obtained diffracted light continuously propagates along the propagation direction of the original signal light after passing through the storage medium, and the reproduced data information is collected by the imaging unit 5.
The servo unit and the imaging unit in this embodiment are the same as the servo optical path and the imaging unit in the embodiment described in fig. 1, and will not be described here.
Fig. 6 provides another embodiment, in which the light source module 1 includes a light path, and the signal light path and the reference light path are overlapped. The signal loading module 2 includes a light path, the signal light path 62 and the reference light path 61 share a relay lens group, and the irradiation positions and angles of the signal light 62 and the reference light 61 can be adjusted simultaneously by moving the second fourier lens 202.
The optical head module 4 includes a light path, and the optical head module includes a dichroic mirror 80, which reflects the servo light 70 and transmits the reference light 61 or the signal light 62, thereby combining the servo light with the reference light and the signal light. The signal light path, the reference light path and the servo light path share one objective lens, and the storage medium is irradiated in a direction perpendicular to the surface of the storage medium through the objective lens.
The signal light spot and the reference light spot having the same p-polarization direction incident to the storage medium 6 are subjected to interference exposure at recording positions where the servo units are positioned in the recording layer 120 of the storage medium to form holograms, thereby completing the recording of information.
During reproduction, the spatial light modulator 190 has no input signal, only the reference light irradiates on the hologram recorded with information in the storage medium, the obtained diffracted light returns along the original signal light direction, and is reflected by the second polarization beam splitter 171 in the signal loading module to the imaging unit module 5, and the reproduced data information is collected by the imaging unit.
The servo unit in this embodiment is the same as the servo optical path in the embodiment described in fig. 1 and will not be described here.
The storage medium in the above embodiment is an optical disc, and includes, as shown in fig. 7, a first substrate 111, a recording layer 120, and a second substrate 112 stacked in this order, and the second substrate 112 has an address layer 113 with a concave-convex structure engraved on a surface thereof close to the recording layer 120. The relief structure of the address layer 113 forms tracks and is provided with data hologram bit marks 114, calibration hologram bit marks 114 and start marks for servo-optically locating the recording position and the reproduction position. And the data holographic bit mark and the calibration holographic bit mark are both a gap on the light path. The data holographic bit marks and the calibration holographic bit marks are located in different regions of the track, respectively.
In the data reading process, the holographic storage optical path system in the above embodiment realizes the calibration of the relative positions of the servo light spot, the reference light spot and the signal light spot in the following manner.
Referring to fig. 8, recording of a hologram for calibration and a data hologram is performed before recording the hologram. The method comprises the following steps:
s11, moving the calibration lens 50 and the second Fourier lens 202 to initial positions so that under the condition that servo light spots are focused on the address layer 113, holograms generated by interference exposure of the reference light 61 and the signal light 62 are effectively located on the recording layer 120 of the storage medium;
s12, fixing the calibration lens 50 and the second Fourier lens 202, moving the storage medium 6 to enable the servo light spot to be positioned at the calibration holographic bit mark, recording the calibration hologram at the calibration holographic bit mark,
s13, moving the storage medium 6 to enable the servo light spot to be located at the other calibration holographic bit mark, and recording the next calibration hologram at the calibration holographic bit mark;
s14, repeating the step S13 for a plurality of times to ensure that a plurality of calibration holograms are successfully recorded;
s15, moving the storage medium to enable the servo light spots to be located at the data holographic bit marks, and recording data holograms at the data holographic bit marks;
s16, moving the storage medium to enable the servo light spot to be located at the other data holographic bit mark, and recording the next data hologram at the data holographic bit mark;
s17, repeating the step S16 to record the whole data hologram;
in step S11, the method for determining the initial positions of the calibration lens 50 and the second fourier lens 202 is: the optical path simulation design ensures that the servo light spot is on the plane of the track of the storage medium 6 (i.e. the address layer), and the interference area of the reference light and the signal light can effectively cover the storage medium 6, and the positions of the collimating lens 50 and the second fourier lens 202 at this time are the initial positions.
Referring to fig. 9, before the data hologram is reproduced, the method for reading the position and the reference beam by moving the storage medium 6, the collimating lens 50, and the second fourier lens 202, and the method for reading the data hologram specifically include:
s21, moving the storage medium 6, moving the optical head 4 to the position near the calibration holographic bit mark, and fixing the position of the calibration lens 50;
s22, adjusting the wavelength of the reference light 61 and finely adjusting the positions of the second Fourier lens 202 and the storage medium 6, and when the diffraction efficiency and the signal-to-noise ratio of the calibration hologram at the calibration holographic bit mark are optimal, fixing the positions of the second Fourier lens 202 and the storage medium and the wavelength of the reference light 61;
s23, moving the position of the calibration lens 50 to enable the servo light spot to be located at the position of the calibration holographic bit mark, and fixing the position of the calibration lens 50;
s24, moving the storage medium 6 to enable the servo light spot to be located at the next calibration holographic bit mark, and reproducing a calibration hologram at the calibration holographic bit mark;
s25, repeating the step S24 for a plurality of times to ensure that the reproduced signal-to-noise ratio of the plurality of calibration holograms meets the minimum signal-to-noise ratio requirement after the second Fourier lens 202 and the calibration lens 50 are fixed;
s26, moving the storage medium 6 to enable the servo light spot to be located at the data holographic bit mark and reproduce a data hologram at the data holographic bit mark;
and S27, repeating the step S26 to reproduce the whole disk data hologram.
As shown in fig. 10, the track-locking error signal and the tangential push-pull signal are detected by the photodetector, and the position of the servo light spot is detected, and when the servo light spot is located in the middle of the calibration holographic bit mark or the data holographic bit mark, both the track-locking error signal and the tangential push-pull signal are located at a zero value between the positive and negative maximum values.
The track locking error signal is used for detecting the condition that the servo light spot deviates from the track, and when the servo light spot is positioned on the central line of the track, the track locking error signal is 0; when the servo light spot gradually deviates from the light track, the track locking error signal gradually tends to a maximum value or a minimum value; when the servo spot is completely off track, the tracking error signal becomes 0.
The tangential push-pull signal is used for detecting holographic position marks of a light path, the holographic position marks can be gaps, and when a servo light spot is positioned in the middle of the gap, the tangential push-pull signal is 0; when the servo light spot gradually deviates from the notch, the tangential push-pull signal gradually tends to a maximum value or a minimum value; when the servo light spot is completely out of the notch, the tangential push-pull signal becomes 0.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific embodiments of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention claims should be included in the protection scope of the present invention claims.

Claims (17)

1. A holographic storage optical path system is characterized by comprising
A storage medium including an address layer and a recording layer;
the address layer consists of a plurality of light paths, and a plurality of data holographic bit marks and calibration holographic bit marks are arranged on the light paths and are respectively used for positioning data holograms for recording data and calibration holograms for calibrating light paths;
the recording unit is used for generating signal light and reference light, irradiating the signal light and the reference light to a storage medium at a certain angle respectively, and performing interference exposure on a recording layer of the storage medium to generate a hologram; the recording unit comprises a signal light path, a reference light path and a relay lens group for adjusting the signal light and the reference light;
the relay lens group comprises a fixed first Fourier lens and a movable second Fourier lens, and the irradiation positions and angles of the signal light and the reference light are adjusted by moving the second Fourier lens;
the imaging unit is used for converting the reproduced signal light diffracted by the reference light into a data page image and collecting the data page image; comprises a fourth Fourier lens for imaging and an image sensor for collecting data page images and analyzing diffraction efficiency and signal-to-noise ratio;
the servo unit ensures that the distance between the optical head of the recording unit and the storage medium is constant in the moving process relative to the storage medium, ensures that the signal light and the reference light move along the track, and can also accurately position the recording or reproducing position, and comprises a servo laser, a beam splitting module, a calibration lens and a signal detection module;
the servo laser is used for generating servo light; the beam splitting module is used for transmitting the servo light beam incident to the storage medium from the laser and reflecting the servo light beam returned by the storage medium to the signal detection module; the calibration lens is used for adjusting the horizontal and vertical positions of the servo light spots; the signal detection module is used for detecting the servo light returned by the storage medium and analyzing the servo light to obtain a servo signal.
2. The holographic storage optical path system of claim 1, wherein the beam splitting module comprises a half-wave plate, a polarization beam splitter and a 1/4 λ plate, the half-wave plate adjusts the servo light emitted by the servo laser to be servo light in a p-polarization direction, the polarization beam splitter transmits the servo light in the p-polarization direction, the 1/4 λ plate adjusts the servo light in the p-polarization direction transmitted from the polarization beam splitter to be servo light in a circular polarization, and adjusts the servo light in the circular polarization reflected back by the storage medium to be servo light in an s-polarization direction, the polarization beam splitter reflects the servo light in the s-polarization direction to the signal detection module, and the signal detection module detects and analyzes the reflected servo light in the s-polarization direction.
3. The holographic storage optical path system of claim 2, wherein the recording unit comprises
The light source module is used for outputting signal light and reference light;
the signal loading module is used for loading the information in the spatial light modulator into the signal light;
and the optical head module is used for enabling the signal light, the reference light and the servo light to be incident to the storage medium at a certain angle, and the signal light and the reference light are subjected to interference exposure on the storage medium to generate a hologram.
4. The holographic storage optical path system of claim 3, wherein the signal loading module comprises an optical path at which the signal light path and the reference light path coincide and share the relay lens group.
5. The holographic storage optical path system of claim 3, wherein the signal loading module comprises two optical paths corresponding to the signal light path and the reference light path respectively, and each of the two optical paths has an independent relay lens group.
6. The holographic optical storage path system of claim 3, wherein the optical head module comprises a dichroic mirror, the dichroic mirror reflecting the servo light and transmitting the read/write light, thereby combining the servo light and the read/write light.
7. The holographic storage optical path system of claim 6, wherein the optical head module comprises a first optical path and a second optical path, the first optical path is a reference optical path through the reference light, the reference optical path at least partially overlaps with the servo optical path, and the reference light and the servo light vertically irradiate the storage medium after passing through the same objective lens.
8. The holographic storage optical path system of claim 6, wherein the optical head module comprises a first optical path and a second optical path, the first optical path is a signal light path via the signal light, the signal light path at least partially overlaps with the servo light path, and the signal light and the servo light vertically irradiate the storage medium after passing through the same objective lens.
9. The holographic storage optical path system of claim 6, wherein the optical head module comprises an optical path where the signal light path and the reference light path coincide, and wherein the signal light, the reference light, and the servo light vertically irradiate the storage medium after passing through the same objective lens together.
10. A method of beam alignment for use in the holographic storage optical path system of any of claims 1 to 9, the method comprising:
s1, before recording a data hologram, recording a calibration hologram at a calibration hologram bit mark on a track of a storage medium; and
s2, before the data hologram is reproduced, the calibration hologram is used, the irradiation position and the angle of the reference beam are changed by adjusting a second Fourier lens in the holographic storage optical path system to ensure that the reproduced signal-to-noise ratio of the hologram is optimal, and meanwhile, the calibration lens is adjusted to ensure that a servo light spot is positioned at a calibration holographic bit mark, and then the data hologram is reproduced.
11. The beam alignment method of claim 10, wherein the diffraction efficiency and the signal-to-noise ratio of the hologram are detected by the image sensor, and the reference beam is considered to be adjusted to be optimal when the diffraction efficiency and the signal-to-noise ratio of the hologram reach a maximum value.
12. The method of claim 11, wherein the method of inscribing the calibration hologram and the data hologram comprises the steps of:
s11, moving the calibration lens and the second Fourier lens to an initial position, so that a hologram generated by interference exposure of reference light and signal light is effectively positioned on a recording layer of a storage medium under the condition that a servo light spot is focused on an address layer;
s12, fixing the calibration lens and the second Fourier lens, moving the storage medium to enable the servo light spot to be located at the position of the calibration holographic bit mark, recording the calibration hologram at the position of the calibration holographic bit mark,
s13, moving the storage medium to enable the servo light spot to be located at the other calibration holographic bit mark, and recording the next calibration hologram at the calibration holographic bit mark;
s14, repeating the step S13 for a plurality of times to ensure that a plurality of calibration holograms are successfully recorded;
s15, moving the storage medium to enable the servo light spot to be located at the data holographic bit mark, and recording a data hologram at the data holographic bit mark;
s16, moving the storage medium to enable the servo light spot to be located at the other data holographic bit mark, and recording the next data hologram at the data holographic bit mark;
s17, repeating the step S16, and recording the whole disc of data hologram.
13. The method for calibrating a light beam according to claim 12, wherein the method for determining the initial positions of the calibration lens 50 and the second fourier lens 202 in step S11 is: the servo light spot is ensured to be on the plane of the track of the storage medium 6 through the light path simulation design, meanwhile, the interference area of the reference light and the signal light can effectively cover the storage medium 6, and the positions of the collimating lens 50 and the second fourier lens 202 at this time are initial positions.
14. The method of beam alignment according to claim 13, wherein the moving storage medium, the alignment lens and the second fourier lens perform alignment of the servo beam and the reference beam before reconstruction of the data hologram, comprising the steps of:
s21, moving a storage medium, moving the optical head to the position near the calibration holographic bit mark, and fixing the position of the calibration lens;
s22, adjusting the reference light wavelength and finely adjusting the positions of the second Fourier lens and the storage medium, and fixing the position of the second Fourier lens and the reference light wavelength when the diffraction efficiency and the signal-to-noise ratio of the calibration hologram at the calibration holographic bit mark are optimal;
s23, moving the position of the calibration lens to enable the servo light spot to be located at the position of the calibration holographic bit mark and fixing the position of the calibration lens;
s24, moving the storage medium to enable the servo light spot to be located at the next calibration holographic bit mark, and reproducing a calibration hologram at the calibration holographic bit mark;
s25, repeating the step S24 for a plurality of times to ensure that the reproduced signal-to-noise ratio of the plurality of calibration holograms meets the highest signal-to-noise ratio requirement after the second Fourier lens and the calibration lens are fixed;
s26, moving the storage medium, enabling the servo light spot to be located at the data holographic bit mark, and reproducing the data hologram at the data holographic bit mark;
and S27, repeating the step S26 to reproduce the whole disc of data hologram.
15. A method of beam alignment according to any of claims 11-14, wherein the position of the servo light spot is detected by detecting the tracking error signal and the tangential push-pull signal by means of a photodetector, and wherein the tracking error signal and the tangential push-pull signal are both at a zero value between positive and negative maximum values when the servo light spot is located in the middle of the alignment holographic bit mark or the data holographic bit mark.
16. The method of claim 15, wherein the tracking error signal is used to detect the servo light spot being off track, and when the servo light spot is on the track center line, the tracking error signal is 0; when the servo light spot gradually deviates from the light track, the track locking error signal gradually tends to a maximum value or a minimum value; when the servo spot is completely off track, the tracking error signal becomes 0.
17. The method of claim 15, wherein the tangential push-pull signal is used to detect a holographic bit mark of a track, and when the holographic bit mark is a notch, the tangential push-pull signal is 0 when the servo light spot is located at the center of the notch; when the servo light spot gradually deviates from the notch, the tangential push-pull signal gradually tends to a maximum value or a minimum value; when the servo light spot is completely out of the notch, the tangential push-pull signal becomes 0.
CN202110673706.4A 2021-06-17 2021-06-17 Holographic storage light path system and light beam calibration method thereof Withdrawn CN115497516A (en)

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US17/843,795 US20220404766A1 (en) 2021-06-17 2022-06-17 Holographic storage optical system and beam calibrating method thereof
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